The present invention relates to a secondary containment unit for closed storage tanks which hold hazardous and non-hazardous liquids, such as petroleum and the like. More particularly, the invention provides an above-ground, transportable containment unit, or dike, which can fit new or existing storage tanks of varying sizes.
National safety and fire standards require that when an above-ground liquid storage tank is used on site, it must be contained within a containment unit in order to contain any spills or leaks which might contaminate the environment or otherwise pose a hazard. These containment units, commonly referred to as "dikes", are generally open-topped tubs and must be a prescribed size so as to accommodate the volume of liquid held by the tank. The open top is prescribed by safety standards which prohibit the use of a cover with the dike. However, an open top permits the entry of precipitation and debris into the dike thus allowing contact with any liquid which may accumulate in the dike. This contamination would prevent any future re-use of the liquid and could pose disposal problems requiring the use of a specialized waste disposal system.
Many of the dikes currently in use do not provide a means for protecting against the collection of precipitation and debris in the dike. For those that do, the protection device typically interferes with the venting, piping or pumping equipment located on the top of the tank.
Further, in order to meet the existing safety standards, many of the existing dikes require 1.5 meters spacing between the dike wall and any surface of the tank while in use. The storage and transportation constraints which result from this oversizing are obvious and often prevent a dike from being transported beyond a minimal distance from site to site. The configuration of these dikes also prevents the units from being easily transported over anything other than a small distance, thus giving the industry a regional nature.
For those secondary units which do provide some means of portability, there is no provision for transporting the dike with the tank in place. While many of the existing units, as disclosed in combination with a tank, may be transported over a short distance those that are secondary units for existing tanks cannot be transported with the tank in place because the dike does not provide means for securing the tank during transport. Therefore, in the event that a storage tank is needed at a different work site, it must be removed from the dike and each piece must be transported separately. This not only represents increased labor and time, it may also result in increased costs to the user of the dike.
U.S. Pat. No. 5,273,180 of Whatley Jr., issued Dec. 28, 1993 relates to a rectangular, open topped containment tank in combination with a liquid storage tank. The containment tank is mounted on skids to facilitate movement across the ground, with a towing bar at least one end of the skids. There is also provided within the containment tank a means for supporting the storage tank in position during usage.
Canadian Patent Application Ser. No. 2,070,939 of Burton published Dec. 11, 1993 relates to a cylindrical inner tank in combination with a rectangular, open topped outer tank. The outer tank is provided with cover means permanently affixed to the walls of the outer tank and extending to the outer surface of the inner tank.
Canadian Patent No. 2,041,556 of Harp issued Mar. 1, 1994, relates to a hooded rectangular containment dike with access means provided in the hood aligned to the expected input or output lines on an inner storage tank.
U.S. Pat. No. 5,287,986 of Frost issued Feb. 22, 1994 describes a cylindrical outer containment unit provided with a cover or hood.
It is an object of the present invention to provide an above-ground secondary containment unit for existing storage tanks of varying sizes and designs which minimizes or prevents the entry of precipitation and debris within the unit while the storage tank is in place yet permits easy access to all pumping, piping and venting on the storage tank. It is a further object of the invention to provide a means for convenient storage of the unit which permits shipment over greater distances than is currently feasible with existing units. Yet a further object is to provide means for securing the storage tank within the unit so as to meet safety standards and eliminate the need to remove the tank prior to transporting the unit.